import SwiftUI

/// Produkt ansehen und ändern, dazu die Chargen korrigieren oder löschen.
struct ProductDetailView: View {
    let product: Product

    @EnvironmentObject private var display: DisplaySettings

    @State private var current: Product
    @State private var lots: [Lot] = []
    @State private var busy = false
    @State private var error: String?
    @State private var status: String?

    // Bearbeitbare Felder
    @State private var name = ""
    @State private var brand = ""
    @State private var packageSize = ""
    @State private var packageLabel = ""
    @State private var datePrecision = "day"
    @State private var groupId: Int?
    @State private var categoryId: Int?
    @State private var groups: [GroupItem] = []
    @State private var categories: [CategoryItem] = []

    // Gegenstände (Non-Food): Bezugsquelle, Link, Lagerorte und eigene Felder.
    @State private var shopId: Int?
    @State private var productUrl = ""
    @State private var shops: [ShopItem] = []
    @State private var locations: [StorageLocation] = []
    @State private var fieldDefs: [FieldDefinition] = []
    @State private var fieldValues: [String: String] = [:]

    @State private var editLot: Lot?

    private let labels = ["", "Glas", "Tüte", "Flasche", "Dose", "Tube", "Becher", "Beutel", "Karton"]

    init(product: Product) {
        self.product = product
        _current = State(initialValue: product)
    }

    var body: some View {
        Form {
            if let status {
                Section { Text(status).foregroundStyle(.green).font(.callout) }
            }
            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }

            ProductPhotoSection(productId: current.id)

            if current.isObject {
                ObjectStockSection(product: current, locations: locations, lots: lots,
                                   onChanged: { await reload() })
            } else {
                Section("Bestand") {
                    LabeledContent("Vorrat",
                                   value: "\(formatAmount(current.stockInArticleUnits)) \(current.articleUnitLabel)")
                    if current.expiredCount > 0 {
                        LabeledContent("Abgelaufen", value: "\(current.expiredCount)")
                            .foregroundStyle(.red)
                    }
                }
            }

            // Beschriftungen links, Werte rechts: Ohne sie las man nur noch
            // "Bratbutter" / "M-Classic" / "450" ohne jeden Zusammenhang.
            Section("Artikel") {
                LabeledField(label: "Name", text: $name)
                LabeledField(label: "Marke", text: $brand)
                if !current.isObject {
                    QuantityField(label: "Packungsgröße", text: $packageSize,
                                  suffix: display.baseUnitLabel(current.baseUnit))
                    Picker("Bezeichnung", selection: $packageLabel) {
                        ForEach(labels, id: \.self) { Text($0.isEmpty ? "Packung (Standard)" : $0).tag($0) }
                    }
                    Picker("MHD-Angabe", selection: $datePrecision) {
                        Text("Tagesdatum").tag("day")
                        Text("nur Monat/Jahr").tag("month")
                    }
                }
            }

            Section {
                CategoryPicker(categories: categories, selection: $categoryId)
            } footer: {
                Text(current.isObject
                     ? "Kategorie bestimmt die Verwaltungsart (Gegenstand) und die eigenen Felder."
                     : "Kategorie: nur für den Überblick in der Artikelliste.")
            }

            if current.isObject {
                Section("Gekauft bei") {
                    Picker("Shop", selection: $shopId) {
                        Text("– unbekannt / mehrere –").tag(Int?.none)
                        ForEach(shops) { shop in Text(shop.name).tag(Int?.some(shop.id)) }
                    }
                    LabeledField(label: "Produktlink", text: $productUrl)
                    if !productUrl.isEmpty, let url = URL(string: productUrl) {
                        Link("Im Onlineshop öffnen", destination: url)
                    }
                }
                if !fieldDefs.isEmpty {
                    Section("Eigene Felder") {
                        ForEach(fieldDefs) { def in
                            ObjectFieldRow(def: def, value: fieldBinding(def))
                        }
                    }
                }
            } else {
                Section {
                    Picker("Gruppe", selection: $groupId) {
                        Text("– keine –").tag(Int?.none)
                        ForEach(groups) { gruppe in
                            Text(gruppe.name).tag(Int?.some(gruppe.id))
                        }
                    }
                } footer: {
                    Text("Gruppe: zählt Bestände mehrerer Marken zusammen. Der EAN-Code "
                         + "wandert bei einem Wechsel mit.")
                }
            }

            Section("Erkennung") {
                LabeledContent("Barcode", value: current.barcode ?? "–")
                if !current.barcodes.isEmpty {
                    LabeledContent("Weitere Codes", value: "\(current.barcodes.count)")
                }
            }

            Section {
                Button(busy ? "Speichern…" : "Änderungen speichern") { Task { await save() } }
                    .disabled(busy || name.isEmpty)
            }

            if !current.isObject {
                Section("Chargen") {
                    ForEach(lots) { lot in
                        Button {
                            editLot = lot
                        } label: {
                            HStack {
                                VStack(alignment: .leading, spacing: 2) {
                                    Text("MHD \(display.formatBestBefore(lot.bestBefore, precision: lot.bestBeforePrecision))")
                                    Text("\(formatAmount(lot.quantity / current.articleUnitFactor)) \(current.articleUnitLabel)")
                                        .font(.caption).foregroundStyle(.secondary)
                                }
                                Spacer()
                                Image(systemName: "chevron.right").foregroundStyle(.tertiary)
                            }
                        }
                        .foregroundStyle(.primary)
                    }
                    .onDelete { indexSet in
                        Task { await deleteLots(at: indexSet) }
                    }
                    if lots.isEmpty {
                        Text("Keine Chargen im Bestand.").foregroundStyle(.secondary)
                    }
                }
            }

            Section {
                // Derselbe Verlauf wie im Listen-Tab, nur auf diesen Artikel
                // gefiltert.
                NavigationLink { HistoryView(productId: current.id) } label: {
                    Label("Verlauf dieses Artikels", systemImage: "clock.arrow.circlepath")
                }
            }
        }
        .navigationTitle(current.name)
        .navigationBarTitleDisplayMode(.inline)
        .sheet(item: $editLot) { lot in
            NavigationStack {
                LotEditView(lot: lot, product: current) {
                    Task { await reload() }
                }
            }
        }
        .task {
            fillForm()
            await reload()
        }
        .onChange(of: categoryId) { newId in
            // Bei Wechsel auf eine Gegenstands-Kategorie deren Felder nachladen.
            Task {
                if let cid = newId, categories.first(where: { $0.id == cid })?.isObject == true {
                    fieldDefs = (try? await APIClient.shared.categoryFields(categoryId: cid)) ?? []
                } else {
                    fieldDefs = []
                }
            }
        }
    }

    private func fillForm() {
        name = current.name
        brand = current.brand ?? ""
        packageSize = current.packageSize.map { formatAmount($0) } ?? ""
        packageLabel = current.packageLabel ?? ""
        datePrecision = current.datePrecision == "month" ? "month" : "day"
        groupId = current.groupId
        categoryId = current.categoryId
        shopId = current.shopId
        productUrl = current.productUrl ?? ""
        fieldValues = Self.stringValues(current.fieldValues)
    }

    private static func stringValues(_ dict: [String: String?]?) -> [String: String] {
        guard let dict else { return [:] }
        var out: [String: String] = [:]
        for (schluessel, wert) in dict { if let wert { out[schluessel] = wert } }
        return out
    }

    private func fieldBinding(_ def: FieldDefinition) -> Binding<String> {
        let key = String(def.id)
        return Binding(get: { fieldValues[key] ?? "" }, set: { fieldValues[key] = $0 })
    }

    private func reload() async {
        groups = (try? await APIClient.shared.groups()) ?? []
        categories = (try? await APIClient.shared.categories()) ?? []
        lots = (try? await APIClient.shared.lots(productId: current.id)) ?? []
        shops = (try? await APIClient.shared.shops()) ?? []
        locations = (try? await APIClient.shared.locations()) ?? []
        if let frisch = try? await APIClient.shared.product(id: current.id) {
            current = frisch
        }
        if current.isObject, let cid = current.categoryId {
            fieldDefs = (try? await APIClient.shared.categoryFields(categoryId: cid)) ?? []
        } else {
            fieldDefs = []
        }
    }

    private func save() async {
        error = nil
        status = nil
        busy = true
        defer { busy = false }
        do {
            if current.isObject {
                // Gegenstände: keine Lebensmittel-Felder, dafür Shop, Link und eigene Felder.
                var fv: [String: String?] = [:]
                for def in fieldDefs { fv[String(def.id)] = fieldValues[String(def.id)] ?? "" }
                current = try await APIClient.shared.updateProduct(
                    id: current.id,
                    ProductUpdateRequest(
                        name: name,
                        brand: brand.isEmpty ? nil : brand,
                        packageSize: nil, packageLabel: nil, datePrecision: nil,
                        groupId: nil, categoryId: categoryId,
                        shopId: shopId,
                        productUrl: productUrl.isEmpty ? nil : productUrl,
                        fieldValues: fv
                    )
                )
                fieldValues = Self.stringValues(current.fieldValues)
            } else {
                current = try await APIClient.shared.updateProduct(
                    id: current.id,
                    ProductUpdateRequest(
                        name: name,
                        brand: brand.isEmpty ? nil : brand,
                        packageSize: Double(packageSize.replacingOccurrences(of: ",", with: ".")),
                        packageLabel: packageLabel.isEmpty ? nil : packageLabel,
                        datePrecision: datePrecision,
                        groupId: groupId,
                        categoryId: categoryId
                    )
                )
            }
            status = "Gespeichert."
        } catch {
            self.error = error.localizedDescription
        }
    }

    private func deleteLots(at indexSet: IndexSet) async {
        error = nil
        for index in indexSet {
            do {
                try await APIClient.shared.deleteLot(id: lots[index].id)
            } catch {
                self.error = error.localizedDescription
            }
        }
        await reload()
    }
}

/// Menge und MHD einer Charge korrigieren.
struct LotEditView: View {
    let lot: Lot
    let product: Product
    var onSaved: () -> Void

    @Environment(\.dismiss) private var dismiss

    @State private var quantity = ""
    @State private var hasDate = false
    @State private var bestBefore = Date()
    @State private var precision = "day"
    @State private var busy = false
    @State private var error: String?

    var body: some View {
        Form {
            Section("Menge") {
                QuantityField(label: "Menge", text: $quantity,
                              suffix: product.articleUnitLabel)
            }

            Section("MHD") {
                Toggle("MHD angeben", isOn: $hasDate)
                if hasDate {
                    Picker("Angabe", selection: $precision) {
                        Text("Tagesdatum").tag("day")
                        Text("nur Monat/Jahr").tag("month")
                    }
                    if precision == "month" {
                        MonthYearPicker(date: $bestBefore)
                    } else {
                        DatePicker("MHD", selection: $bestBefore, displayedComponents: .date)
                    }
                }
            }

            if let error {
                Section { Text(error).foregroundStyle(.red).font(.callout) }
            }

            Section {
                Button(busy ? "Speichern…" : "Speichern") { Task { await save() } }
                    .disabled(busy)
            }
        }
        .navigationTitle("Charge ändern")
        .navigationBarTitleDisplayMode(.inline)
        .toolbar {
            ToolbarItem(placement: .topBarLeading) { Button("Abbrechen") { dismiss() } }
        }
        .onAppear(perform: fill)
    }

    private func fill() {
        quantity = formatAmount(lot.quantity / product.articleUnitFactor)
        precision = lot.bestBeforePrecision == "month" ? "month" : "day"
        if let raw = lot.bestBefore {
            let formatter = DateFormatter()
            formatter.dateFormat = "yyyy-MM-dd"
            if let datum = formatter.date(from: raw) {
                bestBefore = datum
                hasDate = true
            }
        }
    }

    private func save() async {
        error = nil
        guard let menge = Double(quantity.replacingOccurrences(of: ",", with: ".")), menge > 0 else {
            error = "Bitte eine Menge größer 0 angeben."
            return
        }
        busy = true
        defer { busy = false }

        let formatter = DateFormatter()
        formatter.dateFormat = "yyyy-MM-dd"
        let datum = precision == "month" ? bestBefore.startOfMonth : bestBefore

        do {
            // Das Backend rechnet Chargenmengen in Basiseinheiten.
            _ = try await APIClient.shared.updateLot(
                id: lot.id,
                LotUpdateRequest(
                    quantity: menge * product.articleUnitFactor,
                    bestBefore: hasDate ? formatter.string(from: datum) : nil,
                    bestBeforePrecision: precision
                )
            )
            onSaved()
            dismiss()
        } catch {
            self.error = error.localizedDescription
        }
    }
}